This invention relates to a composite fabric which is essentially impermeable to liquids and permeable to vapors, and is particularly suitable for use as a barrier fabric in building construction.
Various types of fabrics are used by the building industry, including those which repel liquid water from the exterior but allow transmission of moisture vapor from the interior. These so-called housewrap products are used with the objectives of increasing personal comfort, improving heating/cooling efficiency, and prolonging the life of the structure. Ideally, the fabric should repel rain and wind, while allowing moisture generated in the interior of the structure to escape, in order to prevent excessive moisture buildup in the interior. Another important criteria is the ability to withstand the effects of weathering and exposure during and after construction.
During construction, barrier fabrics are applied over external and internal walls in a continuous fashion and are used as a temporary cover for windows and doors. The fabric may be exposed to the elements for a considerable period of time prior to the completion of the structure. This causes many existing products to degrade and fail. In addition, the fabric should have enough tear strength and puncture resistance to minimize damage during construction activities. The material is tacked into place, and a frequent problem is the tearing of the fabric from the staples.
Of the currently available materials, none offer all of the combined properties which are desired. Most available products degrade too rapidly or have insufficient barrier properties, or have insufficient tear and puncture resistance.
Various techniques have been proposed for imparting limited porosity to a film or sheet. For example, woven and non-woven materials have been coated with polymeric materials that are filled with substances which cause polymer to form fissures or openings when the filler is dissolved from the structure, or when the coated fabric is worked or heated. In U.S. Pat. No. 4,684,568, a fibrous web is coated with polypropylene resin and the sheet is then calendered to provide limited permeability.